Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Common Stock [Member]	Additional Paid-in-Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive (Loss) Income [Member]	Common Stock in Treasury [Member]	Total
Balance at Dec. 31, 2016	$ 497	$ 575,078	$ 501,761	$ (21,520)	$ (142,500)	$ 913,316
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	0	0	82,151	0	0	82,151
Cash dividends	0	0	(40,104)	0	0	(40,104)
Net issuance of shares to employee and other stock plans	0	(4,608)	0	0	4,335	(273)
Stock-based compensation	0	3,739	(95)	0	0	3,644
Other comprehensive income (loss)	0	0	0	(557)	0	(557)
Balance at Dec. 31, 2017	497	574,209	543,713	(22,077)	(138,165)	958,177
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect adjustment for ASU implementation | ASU 2016-01 [Member]	0	0	2,618	(2,645)	0	(27)
Cumulative effect adjustment for ASU implementation | ASU 2018-02 [Member]	0	0	5,575	(5,575)	0	0
Net income	0	0	112,566	0	0	112,566
Cash dividends	0	0	(43,269)	0	0	(43,269)
Net issuance of shares to employee and other stock plans	0	(2,679)	0	0	2,082	(597)
Stock-based compensation	0	3,936	0	0	0	3,936
Other comprehensive income (loss)	0	0	0	(12,877)	0	(12,877)
Balance at Dec. 31, 2018	497	575,466	621,203	(43,174)	(136,083)	1,017,909
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	0	0	121,021	0	0	121,021
Cash dividends	0	0	(46,010)	0	0	(46,010)
Net issuance of shares to employee and other stock plans	0	(2,968)	0	0	2,087	(881)
Stock-based compensation	0	4,210	0	0	0	4,210
Other comprehensive income (loss)	0	0	0	24,148	0	24,148
Balance at Dec. 31, 2019	$ 497	$ 576,708	$ 696,214	$ (19,026)	$ (133,996)	$ 1,120,397